High-energy excitonic effects in graphite and graphene

TL;DR

This paper uses advanced many-body calculations to reveal strong high-energy excitonic effects in graphite, graphene, and bilayer graphene, significantly impacting their optical absorption spectra and aligning well with experimental data.

Contribution

It provides the first ab initio analysis of high-energy excitonic effects in these carbon allotropes, including predictions for bilayer graphene.

Findings

Strong excitonic effects observed at high energies

Excitonic resonance at 8.3 eV in graphene

Resonance shifted to 9.6 eV in bilayer graphene

Abstract

We present ab initio many-body calculations of the optical absorption in bulk graphite, graphene and bilayer of graphene. Electron-hole interaction is included solving the Bethe-Salpeter equation on top of a GW quasiparticle electronic structure. For all three systems, we observe strong excitonic effects at high energy, well beyond the continuum of \pi -> \pi * transitions. In graphite, these affect the onset of \sigma -> \sigma * transitions. In graphene, we predict an excitonic resonance at 8.3 eV arising from a background continuum of dipole forbidden transitions. In the graphene bilayer, the resonance is shifted to 9.6 eV. Our results for graphite are in good agreement with experiments.